Is it better to have 2 less than great vehicles, or one decent vehicle? (Please read details.)

My husband has two vehicles. A car that he drives daily, and a work truck that he uses to haul a trailer and equipment. Neither are in great shape. The car has no heat (we live in Ohio, and heat is kind of necessary with the coming season) and the truck has a leak in the radiator. These are the only problems that I’m aware of, but there may be more to it that I just don’t know about.
We absolutely can not afford to buy a new car or truck this year.
His proposal is to sell both vehicles, and hopefully buy a newer model truck. He believes that having one (slightly) better vehicle is better than having two not so great vehicles.
I’m inclined to disagree. I feel like he has a backup if one of his vehicles decides to kick the bucket. I also dislike the idea of him combining a personal vehicle and work vehicle into one. That puts a lot of mileage on a truck that we will most definitely be buying used. The cost of fuel also concerns me, when comparing driving a truck to driving a car on a daily basis.
Granted, if something were to happen to the singular truck… I do have a car and it is in great shape. Very reliable, so it isn’t like we would be left without a car at all.

So my question is this: Do you think it is better to get some work done on the two older vehicles and keep them, or is it better to sell both and buy a used truck in (hopefully) better condition than the two vehicles he already owns?
Can you explain why? I really am concerned about fuel efficiency and cost, but my husband says that I don’t really understand how it works (which is feasible). Can someone explain that to me?